The use of video camera and digital video processing techniques for determining and detecting features from the image are well known in the art. The inventors have previously disclosed in PCT Application GB99/03459 a system for detecting smoke in the image. These systems are used as another sensor input for a fire alarm system. Flame is a further component in combustion and it is possible to have a fire event that produces no smoke. An algorithm that detects the presence of flame within a video image provides a further input into the fire detection process.